Dose-Related Visual Outcomes in the Treatment of Choroidal Melanoma with Stereotactic Radiotherapy

Abstract

Introduction Stereotactic fractionated radiotherapy (SRT) in the treatment of choroidal melanoma (CM) may be indicated if the tumour is located close to the optic nerve or is unsuitable for a radiotherapeutic plaque. It is thought that the rate of visual decline and ocular sequelae with SRT is influenced by dose and location of radiation in relation to important visual structures. This study therefore aimed to look at these prognoses with respect to localisation and dose of radiation when treatment of CM with SRT occurs. Methods A retrospective data analysis was conducted on all patients at Dunedin Hospital (DH) from August 2001 to May 2017 and were followed-up for four years. SRT consisted of 50 Gy divided into five fractions over five days to tumours, with 2 mm treatment margins. The primary outcome measure was retention of functional vision – better than Hand Movements (HM) within the treated eye. Secondary outcome measures included: time to non-functional vision (HM or less) in relation to location, dose and tumour thickness, the presence of radiation retinopathy (RR), local and metastatic tumour progression, enucleation, and disease-specific mortality. Results Seventy-five patients were identified in this study. Follow-up was incomplete in ten patients and four patients became deceased within the four-year study period. Twenty-nine patients (48%) retained visual acuity (VA) better than Hand Movements (HM) in the treated eye at four years, thirty-two (52%) of patients did not. Calculated dose to the optic nerve and macula and proximity of the tumour to the optic nerve and macula were not statistically determinative of vision outcomes, although presenting visual acuity was. Fifty-six percent of patients developed radiation retinopathy involving the macula. The local progression, metastatic progression and enucleation rates were 4.6%, 6% and 12.3%, representing three, four and eight patients respectively. Conclusion This study demonstrates that approximately half of patients treated with SRT can expect to maintain functional vision better than HM at four years. The rate of visual decline and final vision outcome are independent of location of the tumour in relation to the optic nerve and macula. Whilst it affirms that SRT achieves high rates of local tumour control and eye retention, preservation of functional visual acuity remains an unpredictable endpoint for individual cases and highlights the therapeutic challenge of this treatment modality.